With it’s single network port, low memory and low CPU speed, a Pi may not seem capable of filtering traffic at a very high bandwidth. This article describes how to make a small filter system that can block IP addresses on the inside or outside of your network while not having any noticeable effect on the network speed. And no, it’s not just blocking the DNS, it’s really blocking the traffic.
Where Geoff Johnson (AKA Hoagie) puts random stuff.